The present invention relates no packing assemblies that prevent leaks around valve stems.
A problem often encountered with quarter-turn valves, which have been in service for some time, is a leak around the valve stem due to wear on the stem packing caused by repetitive opening and closing of the valve. The conventional shape of a stem packing is a cylinder with a hole through the center to receive the valve stem. A gap develops between the stem packing and the valve stem due to uneven frictional wear. This gap allows leaks to occur. It would be desirable, therefore, to equip existing quarter-turn valves with a stem seal assembly such that it does not develop leaks between the stem packing and the valve stem or any other possible leak paths.
A new and novel approach to achieve this goal was shown in U.S. Pat. No. 5,044,606, Wordin, 1991. A tractrix shape on the valve stem was introduced for the stem packing to bear against. The tractrix shape is selected because it provides even and uniform wear on the stem packing as the valve stem rotates against the stem packing. Tests have shown no leaks develop between the stem packing and valve stem after hundreds of thousands of open-close cycles for such a valve. However, the referenced patent is for new valve manufacture and does not lend itself to retrofitting a valve stem packing to existing valves already in service.
Numerous benefits would result from the use of such a stem seal assembly when installed in existing valves. Chemical Plant personal would enjoy increased safety resulting from the positive containment of hazardous or toxic substances. Environmental quality would be enhanced around petro-chemical plants and refineries by the positive containment of volatile substances. Companies could easily comply with Environmental Protection Agency regulations. Stem seal leaks as a source of objectional odors would be eliminated. Power plants would become more efficient by the positive containment of steam. Maintenance costs caused by the need to frequently tighten stem seal packings will be substantially reduced.
Accordingly, it is an object of the present invention to equip existing quarter-turn valves with a stem seal assembly which does not develop leaks between the stem packing and the valve stem.
Additional objects, advantages, and novel features of the invention will be set forth in the description that follows and will become apparent to those skilled in the art or may be learned with the practice of the invention. The objects and advantages of the invention may be realized by means of the instrumentalities and combinations further pointed out in the appended claims.